Nicotinic acetylcholine receptor channels (nAChRs) that contain the α7 gene product (α7-nAChRs) are one of the most abundant types of nicotinic receptors in the vertebrate nervous system. The α7-nAChRs differ from most neuronal nicotinic receptors in that they bind α-bungarotoxin (αBgt) with high affinity and have calcium permeability comparable to N-methyl-D-aspartate (NMDA) receptors. The α7-AChRs modulate various cell processes ranging from synaptic transmission to apoptosis. These receptors appear to be involved in learning and memory, and have been linked to pathophysiological conditions such as schizophrenia. Recent experiments have also shown that the β-amyloid peptide is a ligand for α7-nAChRs, suggesting that α7-nAChR function may be altered during Alzheimer's disease.
The α7 nicotinic acetylcholine receptor subunit was first cloned from chick brain and was later shown to form functional homomeric AChRs when expressed in Xenopus oocytes, and to contribute to functional nAChRs in native cells. However, the composition and stoichiometry of native α7-nAChRs remain to be confirmed, and differences exist in the pharmacological and biophysical properties of α7-nAChRs from different cell types. For example, whereas α7-AChRs in rat hippocampal neurons desensitize rapidly and bind αBgt in an irreversible manner, α7-nAChRs in mammalian autonomic neurons desensitize slowly and recover rapidly from αBgt blockade.
It has been proposed that the heterogeneity in α7-nAChRs may be due to cell-dependent expression of α7 subunit isoforms. This theory was supported by the observation that splice variations of the α7 subunit are detected in human brain and leukocytes. However, most of these α7 isoforms contain a premature stop codon, or form a truncated subunit that is not activated by acetylcholine. While various other ligand-gated ion channels such as 5-hydroxytryptamine 3 (5-HT3) and gamma aminobutyric acid (GABA) receptors have been shown to express functional splice variants with distinct properties, there is little indication that this type of diversity exists in nicotinic acetylcholine receptors.